Transcript Weather & Climate: Introduction

WEATHER AND
CLIMATE
LECTURE 1
Atmosphere: Structure and
Composition
Atmosphere is made up of layers:
1. Troposhere
- decreases by 6.4 degrees Celsius for every
1000m increase in height (Environmental
Lapse Rate)
- contains most of the water vapour, cloud,
dust, pollution
- tropopause: upper limit of the troposhere.
- temperatures remain constant with height
increase
Atmosphere: Structure and
Composition
2. Stratosphere
- steady increase in temp due to ozone
concentration
- winds increase with height
- pressure decreases with height
- stratopause: layer above stratosphere
- no change in temp with increasing height
Atmosphere: Structure and
Composition
3. Mesosphere
- temperatures fall rapidly - no gases or
particles present to absorb radiation
- mesopause: layer above mesosphere where
no change in temperature with height is seen
HEAT/ENERGY BUDGET
Before looking at the earth’s budget, let us
see what happens to incoming solar
radiation:
3 General Processes act upon incoming
radiation:
a) Absorption
b) Radiation
c) Reflection
HEAT/ENERGY BUDGET
Absorption.
- by gases in the upper atmosphere as well
as ice particles and dust
Reflection.
- by clouds and the earth’s surface back to
space
- dependent on the albedo of clouds and
earth’s surface
- gas molecules also scatter radiation back
to space. The rest reaches surface by
diffuse radiation (scattered energy)
HEAT/ENERGY BUDGET
Scattering and Diffuse Radiation
Scattered insolation is either:
Scattered Back to
Space
Absorbed by
earth’s surface as
diffuse radiation
HEAT/ENERGY BUDGET
Incoming radiation converted to heat
energy
- radiates back to the atmosphere
- absorbed by water vapour/carbon dioxide
to retain heat near the surface (Greenhouse
Effect)
HEAT/ENERGY BUDGET
The amount of radiation the earth receives:
A system of inputs and outputs
Balances on the global level, but not
necessarily so on a local scale
HEAT/ENERGY BUDGET
Heat Escapes to
Space
Eg: At night, no incoming radiation, yet
heat is still lost, especially on cloudless
days
- at any one place and time, more radiant
energy is being lost than gained, vice versa
HEAT/ENERGY BUDGET
This can be determined by the net
radiation: difference between all incoming
and outgoing radiation
surplus: radiant energy flowing in faster
than it is flowing out
deficit: radiant energy flowing out faster
than it is flowing in
HEAT/ENERGY BUDGET
What prevents tropics from overheating?
1 Horizontal Heat Transfers
- winds carry heat energy away from the
tropics
2. Vertical Heat Transfers
Radiation, conduction, convection and
transfer of latent heat
- supplementary reading
Factors Affecting Temperature
Amount of insolation varies through time
and space, and from point to point
a) Long-term factors
b) Short-term factors
c) Local influences
Long-Term factors
Height above sea-level
- atmosphere heated from earth’s surface by
conduction and convection
- dependent on surface area of landmass
Atmosphere
Conduction
Convection
Warm, rising
Air
Surface
- as heights increase on mountains, less
land mass present to give off heat by above
process, hence lower temperatures
Long-Term factors
Height above sea-level
- at the same time, pressure/density of air
decreases with altitude
- less air molecules present to absorb and
retain heat, hence as air thins with altitude,
temperatures decrease
Decreasing
Surface
Density of Air
Molecules
with
Increasing
Height
Long-Term factors
Altitude of the sun
- temperatures decrease with decreasing
angle of the sun
-Less loss of energy at
A as ray at A travels
a shorter distance than
B
at B
A
Sun
Long-Term factors
B
A
Sun
Therefore, the higher the latitude (moving
from Poles to Equator), the higher the
temperatures, vice versa
Long-Term factors
Nature of Surface (Land/sea)
- Land and water differ in their abilities to
absorb heat
- specific heat capacity: the amount of energy
needed to raise 1kg of a substance by 1 degree
Celsius
- water has a higher S.H.C. than land/soil
Long-Term factors
Nature of Surface (Land/sea)
- water requires more energy to raise its
temperature by 1 degree Celsius as compared
to continents
- In summer, sea heats up more slowly than
land
- In winter, land loses energy more rapidly
than the sea
Long-Term factors
Nature of Surface (Land/sea)
Illustration of different rates of energy
gain/loss between land and water
Swimming Pool on a hot day:
- air temperatures warm
- water seems to be ‘icy’ cold when you jump
in
A chilly afternoon immediately after a heavy
rain:
- air temperatures cool
- water in the pool seems to be ‘nice and
warm’
Long-Term factors
Nature of Surface (Land/sea)
- Continental areas therefore are more
responsive to temperature changes as
compared to water bodies
- this is also why coastal areas have smaller
annual temperature ranges than inner
continents
Long-Term factors
Prevailing winds
- where winds come from
- and characteristics of surface over which
they blow
Winter:
- winds blowing from sea tend to be warmer
- coastal areas experiencing such breezes will
be warmer than areas not experiencing such
breezes
Long-Term factors
Prevailing winds
Warmer Sea
Breeze
Warms coastal areas.
Warm wind eventually
cools with distance into
continents
Cold Surface (Winter)
Inner Continents will be colder than coastal areas
even if they may be within the same climatic
region
Long-Term factors
Ocean Currents
N. Pole
Warm
Currents
Cold
Currents
Equator
S. Pole
Short-term factors
Seasonal Changes
- due to earth’s tilt, Northern Hemisphere
receives more insolation during Summer
solstice (21 June) than Southern Hemisphere
- Northern Hemisphere receives less insolation
during Winter Solstice (22 December)
N
S
Earth’s axis on
which it rotates
not on the South
Pole
But is tilted at
an angle
Short-term factors
Earth during Winter
Solstice
Equator
- Northern Hemisphere - less insolation (cooler ie
Winter)
- Southern Hemisphere - more insolation (warmer ie
Summer)
Short-term factors
Earth’s Elliptical Orbit around the
sun therefore sets up the different
seasons
Spring
Summer
Autumn
Winter
Short-term factors
Length of Day and night
- areas experiencing longer days tend to have
higher temperatures
Equator:
- Equal lengths of day and night every 24 hours
Poles:
- experience 24 hours of darkness for parts of
winter
- during summer, experience up to 24 hours of
day
Local Influences on Insolation
Slope Aspect
- northern hemisphere: north-facing slopes
(adret) receive less sunshine
- cooler than south-facing slopes (ubac)
In addition, steeper slopes receive more
insolation due to their higher angle of
incidence
Local Influences on Insolation
Cloud Cover
- reduces both incoming and outgoing
insolation
- thicker cloud cover, more absorption,
reflection, scattering and terrestrial
radiation (radiation back to space) during
daytime
- cooler temperatures during day with thick
cloud cover, higher with no/little cloud
cover
Local Influences on Insolation
Cloud Cover
- Night:
- Thick cloud cover during night time can
act as an insulating blanket to trap heat
- lack of cloud cover during the night, loss
of heat from surface by terrestrial radiation,
cool/cold temperatures
Local Influences on Insolation
Urbanisation
- alters the albedo of natural landscape
- buildings, concrete and black roads tend
to reflect less insolation and therefore
absorb more heat
- hence higher temperatures in urban areas
than grass or natural landscape
Finito